I've just did fresh installs of the ADT bundle (20130522) and the Android Studio. (because my eclipse install got screwed up again, but that's another story.)
In either version, when I launch the SDK Manager, I don't have any system images for 2.2, only an x86 image for 2.3.3, and no images for 3.0, 3.1, and 3.2.
I couldn't find any official word as to why they've been removed. Is there now a better way to test on those platforms rather than by using the emulator images?
Check the "Obsolete" checkbox, towards the bottom of your SDK Manager window, and you should see them.
More specifically, up until Android 4.0 (or thereabouts), the ARM emulator image was not broken out into a separate download, and so you get that from the base "SDK Platform" download.
Why would people expect the ARM image to be part of the SDK platform for <4.0, when it is broken out separately for 4.0+
Well, for those of us graybeards who have been developing for Android for a while, it's second nature... :-)
More seriously, I suspect they did not want to attempt to repackage the older releases. Bear in mind that the only available platform for Android was ARM up until about 2.3, and so having a separate ARM image download would have seemed odd back in the beginning.
来源：https://stackoverflow.com/questions/17308874/sdk-manager-is-missing-older-android-system-images-for-emulator